1. Field of the Invention
The present invention relates to metal drums (e.g., cylindrical) of relatively thin wall thickness (e.g., 14-24 gauge), such as the standard 55-gallon steel drum and the like, and more particularly the present invention relates to an improved drum closure formed entirely from the drum stock which eliminates the need for rubber or like seal material, and the extra cost of drum closure fittings. Further, the present invention relates to an improved method of forming a drum closure, which is formed into a cylindrical flange from the material of the drum top or lid portion, and rolling a thread onto the flange.
2. General Background
Closures for thin wall drums normally consist of a steel bushing or flange having an internally threaded cylindrical neck with a sealing gasket therearound. At times, the neck has a laterally extending polygonal base surrounding its lowermost end. In some drum closures, a perforated container wall section overlies the neck flange and base. An upper unthreaded portion of the flange neck can be beaded outwardly over the surrounding drum stock so as to permanently secure the flange in place. This type of prior art closure is typically completed with the threaded engagement of a closure plug and the application of an overlying tamper-resisting drum seal.
The problem with prior art types of drum closures is that as the rigidity of the drum stock immediately surrounding the closure flange is diminished, a consequent reduction in resistance to turning torque occurs between the flange and the drum stock. Typically, high-torque resistance for proper seating and unseating of the closure plug is essential to good closure performance.
Various attempts have been made to improve the torque characteristics on the flange fitting insertions in light-gauge, e.g., 14-24 gauge, drums. Some manufacturers of thin wall drums have attempted to solve the problem of a suitable drum closure by providing reinforcing collars designed to overly the drum stock section immediately surrounding the flange in order to achieve necessary strength. Such a complicated solution, however, dramatically raises the cost of the drum. Indeed, the requirement of a separate flange fitting as part of the drum closure in and of itself can be a significant item of expense. The separate flange fittings can be dislodged, reducing the torque needed to turn the fitting, rendering the drum useless.
Another problem in the industry is the cleaning of drums after they are emptied. Hazardous, oily, and chemical products left in drums by the primary user create a significant pollution problem during cleaning of the drums. Many drum closures use flange fittings that are positioned to protrude inwardly and downwardly from the drum top. This protrusion prevents full emptying of the drum and the seam around the insert contain material that cannot be removed and thus contaminates the contents of the next load on reconditioned drums.
Some materials can only be removed from the drum by intense heat or burning in order to melt the contained product from the interior of the drum. This heating can destroy rubber which is often used as a seal as part of the fitting and drum stock assembly.
For containing corrosive chemicals and products, a common practice is to provide an interior coating for the drum container which is resistive to the corrosive effect of the intended content. This interior coating is traditionally called a lining. The lining must be under any drum fitting to prevent corrosive fluid from corroding or eating the drum metal under the fitting. Due to the working required to crimp the fitting in or install the fitting, the lining under the fitting is also subject to damage. Therefore the practice is to overcoat the entire fitting a second time, hoping that some of that coating, lining, paint, or the like will seal the fitting and adjacent metal. The area at the fitting is usually still inferior to the rest of the lined drum container surfaces.
Another problem is that the drum manufacturer must either inventory the fittings, or have a delay time or added expense because the manufacturer must buy pre-painted fittings.
Another problem is that the thread formed on the opening must be continuous so that a good closure seal can be made with a closure plug.
The advantage with the present invention is that any standard head can be painted and cured and a lined head is provided in one operation, because the problems with the separate fittings do not exist. There is no crack or break around the fitting, nor is it necessary to inventory any fittings. The drum fitting of the present invention can be easily lined in a single step and without special equipment, therefore providing a superior product at a reduced cost.
U.S. Pat. No. 2,686,610, issued to E. V. Sharpnack, Sr., entitled "Metal Drum," shows a typical common metal drum as presently used in the industry. These drums are typically standardized to capacities of, for example, 15-gallon, 30-gallon and 55-gallon. Such drums are commonly used to carry an abundance of liquid products, including oil, petrochemicals, chemicals, solvents, water, and the like.
Drums are constructed of a usually cylindrical side wall and a flat circular top and a flat circular bottom. Drums usually have a relatively small three-fourths to two inch (3/4"-2") threaded opening through which material can be dispensed from the drum as well as added to the drum.
An early patent which discusses a process of making metallic barrels is the Mauck et al. U.S. Pat. No. 1,095,014, entitled "Process Of Making Metallic Barrels".
An example of a prior art drum closure which uses an extra fitting mated to the drum stock can be seen in U.S. Pat. No. 4,004,709, issued to V. Simkus, entitled "Drum Closure." In the Simkus patent, a threaded closure construction is disclosed for light-gauge steel drums. The closure provides an internally threaded closure flange mechanically secured within a suitably formed container wall opening. The flange is formed with a cylindrical neck internally threaded throughout its lower extent and surrounded exteriorly by a polygonally shaped base. A resilient sealing gasket tightly surrounds the flange neck at is juncture with the flange base. A perforated drum stock section is formed to overlie and closely surround the flange neck and base in a torque-resisting manner with the upper end of the flange neck beaded outwardly over the surrounding drum stock. The closure is completed with the threaded engagement of a closure plug and application of an overlying tamper-resisting drum seal.
A liquid dispensing container construction is the subject of U.S. Pat. No. 4,032,047, issued to C. Wilson. The apparatus shows a spigot device carried by one of the end portions of a container for dispensing liquid from within the chamber, and a closeable filler device for the chamber is provided in the other of the end portions.
The Wilson U.S. Pat. No. 4,034,896, entitled "Diaphragm Controlled Garden And Orchard Sprayer," discloses a canister having upper and lower flat top portions. The top includes an upper threaded opening having a plug which attaches thereto.
U.S. Pat. No. 3,365,926, issued to Price and entitled "Manufacture Of Plate Metal Parts With Intregral Threaded Fasteners." A plate steel member having a projecting relatively long integral sleeve with concentric sleeve surfaces and a uniform sleeve thickness is made by forming a hole cylindrical throughout its length in a plate blank, extruding a sleeve from metal surrounding the hole under confined compression throughout extrusion flow of the metal, removing the pressure, and then forming a frusto-conical shaped shoulder between the internal sleeve opening and the top plate surface by further downward applied extrusion pressure which sets the metal in the sleeve. The sleeve may be threaded with true and undistorted threads having at least 75% full thread profile capable of resisting torque-tension loading without permanent deformation 30% in excess of the strength of the threads cut in the same steel and requiring a thicker sleeve wall, by removing a thin skin of work-hardened metal from the inner sleeve surface, and then roll-tapping threads by displacement of metal without metal loss throughout the length of the sleeve in the internal sleeve surface. The threaded sleeve member may be incorporated as a component of a composite metal-rubber product by molding an extrusion formed sleeve member before threading with and bonding it to the rubber, then removing the rubber flash from the interior of the sleeve at the same time that the thin skin of work-hardened metal is removed from the inner sleeve surface, and then roll-forming the threads.
A Japanese reference discloses a segmented die apparatus for forming a threaded closure opening of a drum.
The present invention is an improvement to the above patents and to the prior art, providing a simple yet effective drum closure in a light-gauge (14-24 gauge) drum using only the drum stock material, eliminating the need for extra drum flange fittings and the like thus solving the problem of drum stock to fitting torque strength, and the problem of full emptying of drums prior to cleaning and painting. Further, the present invention eliminates the problem of mating a separate flanged fitting to the drum with rubber and like seals which can be destroyed during intense heating of the drum (often associated with cleaning residuals from the drum). Since the fitting of prior art drums is a separate part, they can be easily loosened or dislodged.